Solid-state memory devices have become quite popular due to several advantages over typical active memory devices. First and foremost, the solid-state memory device comprises no moving parts, so it consumes less power and provides robust reliability. Moreover, solid-state memory devices are resistant to mechanical stress, such as impacts and vibration.
One type of memory used for solid-state memory devices is the flash memory device. The flash memory device may be based upon NAND or NOR logic gates, for example. For example, U.S. Patent Application Publication No. 2009/0080236 to Nakamura discloses a memory device. The memory device comprises a plurality of memory cells, and bit lines coupled to each memory cell. The memory device provides a supply voltage to each of the memory cells via the bit lines. Flash memory writing may be implemented by erasing a bank of memory and then programing the desired words into the memory. Because of the banc erasing and programing, flash memory programming may exhibit low granularity.
Another approach to solid-state memory is a phase-change memory. These devices, rather than using the floating gate approach of flash memory, use chalcogenide glass for storing data. In particular, chalcogenide glass may be forced to take either amorphous or crystalline form by exposing it to a prescribed level of heat. The current state is detected by detecting the resistivity of the chalcogenide glass, which predictably varies based upon the form thereof. In phase-change memory the granularity is bit by bit.